1. Field of the Invention
This invention relates to a chemically amplified positive resist composition-which is highly sensitive to actinic radiation such as deep-UV, electron beam and X-ray, can be developed with alkaline aqueous solution to form a pattern, and is thus suitable for use in a fine patterning technique.
2. Prior Art
As the LSI technology tends toward higher integration and higher speed, further refinement of pattern rules is required. The current patterning technology mostly relies on light exposure which is now approaching to the essential limit of resolution which is dictated by the wavelength of a light source. It is generally recognized that in light exposure using g-line (wavelength 436 nm) or i-line (wavelength 365 nm) as a light source, a pattern rule of about 0.5 .mu.m is the limit. For LSIs fabricated by such light exposure technique, a degree of integration equivalent to 16 mega-bit DRAM is the limit. At present, LSIs fabricated in the laboratory have reached this stage. It is urgently required to develop a finer patterning technique.
Under such circumstances, deep-ultraviolet lithography is regarded promising as the next generation of fine patterning technology. The deep-UV lithography is capable of working on the order of 0.3 .mu.m or less. If a less light absorbing resist is used, it is possible to form a pattern having a side wall nearly perpendicular to the substrate.
Chemically amplified, positive working resist materials were recently developed using acid catalysts as disclosed in JP-B 2-27660, JP-A 63-27829, U.S. Pat. Nos. 4,491,628 and 5,310,619. While a high illuminance KrF excimer laser can be utilized as a deep-UV light source, these materials have high sensitivity, resolution and dry etching resistance and are promising as resist materials especially suited for deep-UV lithography.
The chemically amplified, positive resist materials being known include those of the two-component system comprising an alkali-soluble base resin and a photoacid generator and those of the three-component system comprising an alkali-soluble base resin, a photoacid generator, and a dissolution rate inhibitor having an acid labile group.
JP-A 62-115440 discloses a resist composition comprising poly-p-tert-butoxystyrene and a photoacid generator. Similarly, JP-A 3-223858 discloses a two-component system resist composition comprising a resin having a tert-butoxy group in its molecule and a photoacid generator and JP-A 4-211258 discloses a two-component system resist composition comprising a polyhydroxystyrene containing a methyl, isopropyl, tert-butyl, tetrahydropyranyl or trimethylsilyl group in its molecule and a photoacid generator.
Furthermore, JP-A 6-100488 proposes a resist composition comprising a polydihydroxystyrene derivative such as poly[3,4-bis(2-tetrahydropyranyloxy)styrene], poly[3,4-bis(tert-butoxycarbonyloxy)styrene], and poly[3,5-bis(2-tetrahydropyranyloxy)styrene] and a photoacid generator.
Since the base resins used in these resist compositions have a single acid labile group, such a resist composition forms a pattern which tends to have a T-top configuration if the acid labile group is a strong acid-decomposable one such as a tert-butyl and tert-butoxycarbonyl group. On the other hand, if the acid labile group is an alkoxyalkyl group such as ethoxyethyl which is decomposable with weak acid, the resist composition would be less satisfactory in sensitivity and resolution and form a pattern which will become extremely thin with the lapse of time from exposure to heat treatment.
None of the resist compositions thus far proposed are practically satisfactory. There is a desire to overcome these problems.